The present invention relates in general to a still or motion picture camera of the type having an objective cooperating with a reflex viewfinder which includes a deflection member for light rays passing through the objective, and an active infrared rangefinder which includes a receiver provided with an infrared light sensing element such as a photodiode and an infrared light reflecting mirror arranged in the path of light rays passing through the objective and the viewfinder, and a rangefinder transmitter transmitting infrared light onto a selected object to be photographed, the infrared image in the light rays passing through the objective and the viewfinder being focussed on the infrared image plate.
In a known photographic camera of the aforedescribed kind (DE-OS No. 29 36 104), the mirror surface for reflecting infrared rays is arranged between the light rays deflecting member in the form of a swivelling mirror and the image plane of the viewfinder. The viewfinder image is focussed on a ground glass screen located in the viewfinder image plane and converted via a pentagonal prism into an upright image visible in the viewfinder eyepiece. The mirror surface which reflects infrared light is permeable to the remaining light spectrum, screens the infrared image out of the viewfinder light beam, and focusses this infrared image onto the infrared sensing element, such a photodiode.
In many cases, particularly in compact, small-format mirror reflex cameras, the free space between the ground glass screen in the viewfinder image plane and the swivelling or swingable mirror is frequently insufficient for accommodating the additional infrared light reflecting mirror surface.
A space-saving arrangement of the infrared light reflecting mirror surface has been already devised in which a separate infrared light mirror is provided in proximity to the light reflecting swingable mirror of the camera, and the photodiode is located on the ground glass screen outside the field of the viewfinder image. The reflecting mirror of the camera in this case must be transparent to infrared light, whereas the infrared light reflecting mirror is inclined at an angle over the reflecting mirror so as to reflect the infrared image on the photodiode provided on the ground glass screen.
It has also been devised to provide, instead of the two mirrors, a single prismatic mirror whose front side reflects visible light but is transparent to infrared light, and whose back side reflects the infrared light. The reflection of the infrared light in the glass material of the prismatic mirror contributes to deviation of the infrared light, and consequently the deflection angle of the infrared mirror surface to the reflecting mirror surface for visible light is larger than in the preceding example, when two separate mirrors are employed.
Both of the above examples of a space-saving arrangement of the infrared light reflecting mirror surfaces have the disadvantage that, together with the reflecting mirror during the film exposure, the infrared light reflecting mirror must also be swung out. The inertia of the latter swingable arrangement of reflecting mirrors, however, is substantially larger than the inertia of the mirror in a normal single mirror reflect camera, and the speed of movement of such mirror arrangement is slower than is desirable.